The present invention relates to a rolling-bearing unit for supporting a wheel of an automobile such that it rotates freely with respect to the suspension, as well as detects the rotation condition of the wheel contributing to stable movement of the automobile.
The rolling-bearing unit has been used in order to support a wheel of an automobile such that it rotates freely with respect to the suspension. Also, it is necessary to detect the rotation speed (rpm) of the wheel in order to control an anti-lock brake system (ABS) or traction control system (TCS).
Therefore, recently, supporting the wheel such that it rotates freely with respect to the suspension, as well as, detecting the rpm of the wheel, has widely been performed by employing a rolling-bearing unit with rpm sensor in which a rpm detection device has been installed in the rolling-bearing unit.
FIG. 1 shows one example of the prior art construction of the rolling-bearing unit with an rpm sensor for supporting a wheel, used for this purpose. This rolling-bearing unit with rpm sensor for supporting a wheel supports a rotating race or hub 2, that rotates during use in the state where the wheel is attached to the rotating race or hub 2, such that it rotates freely inside an outer race or stationary race 1 that does not rotate during use in the state where it is supported by the suspension.
In addition, it detects the rpm of a sensor rotor 3, that is attached to part of the hub 2, through the use of an rpm detection sensor 5 that is supported by a cover 4 that is attached to the outer ring 1. In the example in the figure, ring-shaped sensor, that faces the sensor rotor 3 all the way around its circumference, is used as this rpm detection sensor 5.
Also, in order to support the hub 2 such that it rotates freely, a plurality of outer-raceways 6 are formed around the inner peripheral surface of the outer race 1. In addition, inner-raceways 9 are formed around the outer peripheral surface of the hub 2 and around the outer peripheral surface of an inner-race 8 that fits around the hub 2 and is attached to the hub 2 by a nut 7 to form the aforementioned rotating race. Moreover, there is a plurality of rolling elements 10 located between each of the respective inner-raceways 9 and outer-raceways 6 and held by retainers 11, respectively, such that they rotate freely, and they rotatably support the hub 2 and inner race 8 inside the outer race 1.
On the axially outer end of the hub 2 (the end on the outside in the direction of width when installed in the automobile, left end in FIG. 1) a flange 12 is formed on the portion that protrudes in the axial direction from the axially outer end of the outer race 1 for attaching to the wheel. Also, on the axially inner end (the end on the inside in the direction of width when installed in the automobile, right end in FIG. 1) there is an installation section 13 for attaching this outer race 1 to the suspension.
The space between the opening on the outer end of the outer race 1 and the outer peripheral surface in the middle of the hub 2 is covered by a seal ring 14. In the case of a rolling-bearing unit for a heavy automobile, tapered rollers may be used in the place of the balls in the figure as the rolling elements 10.
In order that an rpm sensor is installed in this rolling-bearing unit, the sensor rotor 3 is fitted around the outer peripheral surface on the inner end of the axially inner race 8 in the portion away from the inner-raceway 9. This sensor rotor 3 is formed into an entirely ring shape by plastic processing of a magnetic metal plate such as low carbon steel sheet, and comprises a cylindrical section 15 to be detected and a cylindrical section 16 for support that are concentric with each other. Of these, the cylindrical support section 16 is attached to the axially inner end of the inner race 8 by fitting it tightly around the inner end of the inner race 8. Moreover, by forming several slit-shaped through holes in the detected cylindrical section 15 such that they are long in the axial direction of the detected cylindrical section 15 and such that they are uniformly spaced around in the circumferential direction, the magnetic characteristics of the detected cylindrical section 15 changes alternately and uniformly around in the circumferential direction.
Furthermore, the cover 4 is securely fitted on the opening on the inner end of the outer race 1 so as to cover the detected cylindrical section 15 of the sensor rotor 3, and it covers the opening on the axially inner end of the outer race 1. The cover 4 made by plastic processing of sheet metal comprises a cylindrical fitting section 18 that freely fits inside the opening on the axially inner end of the outer race 1, and a cover plate 19 that covers the opening on this inner end. The detection sensor 5 is securely held inside this cover plate 19. There is a through hole 20 formed in an outer peripheral portion of the cover plate 19, and a connector 21 for receiving the output from the rpm detection sensor 5 runs through this through hole 20 to outside the cover 4. With the rpm detection sensor 5 held and attached inside the cover 4 in this way, the detected portion, located on the outer peripheral surface of the rpm detection sensor 5, faces the inner peripheral surface of the detected cylindrical section 15 of the sensor rotor 3 through a small gap therebetween.
When using the rolling-bearing unit with rpm sensor for supporting a wheel described above, the installation section 13 that is formed around the outer peripheral surface of the outer race 1 is fastened to the suspension (not shown) by a bolt (not shown), and a wheel (not shown), is fastened to the flange 12 that is formed around the outer peripheral surface of the hub 2 by fastening the studs 22 formed in the flange 12. In this way, the wheel is rotatably supported with respect to the suspension.
In this state, when the wheel rotates, the area on the end on the detected portion on the rpm detection sensor 5 is alternately passed by the through holes 17 formed in the detected cylindrical section 15 and by the columns located between pairs of adjacent through holes 17 in the circumferential direction. As a result, the density of the magnetic flux that flows inside the rpm detection sensor 5 changes and thus the output of the rpm detection sensor 5 changes. The frequency of the changing output of the rpm detection sensor 5 is proportional to the rpm of the wheel. Therefore, by sending the output from the rpm detection sensor 5 to a controller (not shown), it is possible to sufficiently perform ABS or TCS control.
In other words, the output of the rpm detection sensor 5 is compared with the output of the acceleration sensor located separately on the car body, and when the two sensors do not match in the output thereof, it is determined that slippage is occurring in the area of contact between the outer peripheral surface of the tire and the road surface, and thus ABS or TCS control is performed.
That is, when the deceleration of the wheel found based on the output of the rpm detection sensor 5 is larger than the deceleration of the automobile detected by the acceleration sensor during braking, it is determined that slippage is occurring, and the hydraulic pressure of the wheel cylinder of the brake device is controlled to prevent rotation of the wheel from stopping before the automobile stops, and thus making it possible to maintain stable movement of the automobile.
On the other hand, during acceleration, when the acceleration of the automobile found from the acceleration sensor is smaller than the acceleration of the wheel found based on the output of the rpm detection sensor 5, it is determined that slippage is occurring, and by braking the wheel or throttling (lowering) the engine output, it is possible to prevent slippage between the outer peripheral surface of the tire and the road surface, and to stabilize the movement of the automobile.
With the prior art rolling-bearing unit with rpm sensor for supporting a wheel described above, it is possible to maintain stable movement of the automobile during braking and acceleration, however, in order to be able to maintain stability in more severe conditions, it is necessary to obtain more information of things that will affect the stability of the moving automobile in performing brake of engine control.
On the other hand, in the case of ABS or TCS which uses the prior art rolling-bearing unit with rpm sensor, so-called feedback control, where slippage of the tire with the road surface is detected, is performed for controlling the braking or acceleration. Therefore, braking or engine control is a little delayed, so that improvement is desired from the aspect of performance under severe conditions.
In other words, in the case of the prior art construction, it is not possible to prevent, with the so-called feedforward control, slippage from occurring between the tire and road surface and to prevent, so-called oneside braking, that is caused by extreme differences in braking force on the left and right of the automobile. Furthermore, in the case of a truck or the like with poor load conditions, it is not possible to prevent stability from becoming poor. The rolling-bearing unit for supporting a wheel of this invention, was invented with these problems in mind.
The present invention provides a rolling bearing unit for supporting a wheel, wherein a vibration sensor and rotation speed sensor are combined to improve stability in acceleration and deceleration.